In a trickle flow reactor, liquid trickles through one reaction bed or through a number of reaction beds arranged one below the other and gas flows co-currently or counter-currently with the liquid through the reaction bed(s). Such reactors are used in the chemical industry and in the petroleum refining industry for hydrocarbon processing, especially hydroprocessing such as catalytic dewaxing, hydrotreating and hydrocracking. Reference herein to hydrotreating is to hydroprocessing under relatively mild process conditions, for example hydrodesulphurisation, hydrodenitrogenation, hydrogenation or hydrofinishing.
Such a reactor comprises at least one reaction bed, typically a bed of catalyst particles, resting upon a support grid. Liquid effluent, formed in the reactions occurring in the catalyst bed, flows through the support grid to the subsequent catalyst bed or reactor outlet.
Such reactors typically contain a distribution device to distribute the liquid entering the reactor via the reactor inlet homogeneously over the upper reaction bed or to distribute the liquid effluent of a reaction bed homogeneously over the next lower reaction bed.
Distributor trays wherein gas and liquid pass co-currently through the same downcomer(s) are known in the art. Reference is made to U.S. Pat. Nos. 6,180,068, 4,836,989, EP 715 544, U.S. Pat. Nos. 4,140,625 and 6,093,373. In U.S. Pat. No. 6,093,373 for example, an apparatus for mixing vapour and liquid reactants within a column is disclosed. The apparatus comprises a final distributor tray consisting of a plurality of chimneys designed to create shear between the gas and liquid phases.
Disadvantages of trays wherein gas and liquid pass through the same downcomer is that they are not suitable to operate under conditions wherein there is no or a very low gas pressure drop across the tray and that they are not suitable for countercurrent operation, i.e. for operation wherein the gaseous and liquid reactants flow countercurrently with respect to each other.
In U.S. Pat. No. 5,799,877, a distributor tray is disclosed that comprises a plurality of gas and liquid spray distributors. Each gas and liquid spray distributor has separated gas and liquid conduits. In each distributor, the gas and liquids conduits are co-axial, i.e. having the same longitudinal axis, with the liquid conduit surrounding at least part of the gas conduit to define an annular space for downward liquid flow. The gas exits its conduit as a gas core surrounded by downflowing liquid. The gas expands and contacts the surrounding liquid to spray it on the catalyst bed below. A splash plate is located below the gas and liquid exit of each distributor to assist in distributing the downflowing liquid spray across the catalyst bed below.
The tray disclosed in U.S. Pat. No. 5,799,877 is a distributor tray for cocurrent gas and liquid flow, since the downflowing gas is needed to create a liquid spray. The tray is not suitable for countercurrent operation.
In WO 99/00182 a distributor tray for a countercurrently operated hydroprocessing reactor is disclosed. Liquid is distributed over the underlying reaction bed by means of a distribution tray having a plurality of short tubes for liquid passage. Gas vents in the tray allow passage of the upward moving treat gas. A disadvantage of the distribution tray disclosed in WO 99/00182 is that the liquid will not be spread over the whole surface area of the underlying catalyst bed.
There is a need in the art for a distribution device that can achieve uniform spreading of the liquid over the underlying reaction bed, both in co-current and in countercurrent operation.